Gas turbine engine rotor blade tip clearances have a significant influence on engine performance. Leakage past the blade tips can be minimized by maintaining a desired or predetermined clearance between the blade tips and the case. Clearance can be selectively increased during specific portions of the flight to avoid contact between blade tips and the case. Thrust specific fuel consumption of the engine is thereby reduced and engine durability is increased.
Active clearance control (ACC) systems are frequently used to control blade clearance. ACC systems can provide cooling to certain areas of the engine case to shrink the engine case around the rotating compressor blades and thereby minimize the clearance between the case and blade tips.
Current ACC systems utilize manifolds having a uniform and consistent distribution of cooling holes. Such manifolds provide cooling air from outside of the engine case to the engine case itself. It may be desirable to provide an ACC with an improved manifold capable of tailoring cooling to particular portions of the engine case.